The present invention relates to a base-station cell design method, an apparatus and a program thereof in a radio communication system, and more particular to a base-station cell design technique such as base-station layout and base-station parameter setting in a mobile communication system.
A conventional base-station cell design technique will be explained by use of FIG. 17. Base-station candidates are arranged in locations displayed with black squares A02 to A06 on a service area A11 to evaluate a rate of areas A01, and A07 to A10 to be covered by the above base-station candidate group to a service area A11, i.e. an area coverage ratio. Similarly, the area coverage ratio is evaluated for the other arrangement location as well to repeat its evaluation until a base-station arrangement pattern in which a desired area coverage ratio is reached is obtained. In the event of making base-station installment of a trial-and-error optimal-arrangement search type like this, a detailed evaluation of a radio-wave propagation characteristic extending over the entire service area is required base station by base station whenever the base-station arrangement is given.
As another technique, there is a technique that a human being pre-narrows down a pattern to be evaluated for realizing a reduction in the computation time (for example, a patent document 1). Also, as yet another technique, there is a technique of employing genetic algorithm for realizing a reduction in the time required for the optimal-arrangement research (for example, a patent document 2). A further additional technique will be explained by employing FIG. 18 (for example, a non-patent document 1). In this non-patent document 1 was disclosed a base-station cell design technique of pre-arranging the regularly placed base stations in the locations indicated with black small points B02 within a service area B01 to sequentially delete the base stations that did not contribute to an increase in a covered area. It is required to make a high-precision radio-wave analysis within all the service area for all base-station candidates pre-arranged regularly.
[PATENT DOCUMENT 1]
JP-P1996-317458A (page 2 to 3, FIG. 1 to FIG. 3)
[PATENT DOCUMENT 2]
JP-P2001-285923A (page 2, FIG. 1)
[PATENT DOCUMENT 3]
JP-P2002-107397A
[NON-PATENT DOCUMENT 1]
M. Kamenetsky, et. al. “Coverage Planning for Outdoor Wireless LAN System”, 2002 International Zurich Seminar on Broadband Communication Access, Transmission, Networking, Feb. 2002, pp 49-1 to 49-6
[NON-PATENT DOCUMENT 2]
Proc. of International Symposium on Antennas and Propagation Society, 1991, vol. 3, pp. 1540–1543
It has been generalized that the base-station cell design in a cellular system employs a specialized tool; however a covered area of an access point (AP: equivalent to the base station) is extremely narrow, a simple propagation-loss estimation equation employed in a conventional cellular system design is impossible to apply in a wireless LAN system to be installed in the environment where a lot of propagation disturbing objects such as a building exist in a line-of-sight propagation area of a radio wave, and a detailed radio-wave analysis, which took a microscopic structure such as a geographical feature of a target area and the building into consideration, is required.
A ray tracing technique is commonly used as a technique of the high-precision radio-wave analysis; however upon employing the cell design technique of the trial-and-error optimal-arrangement search type as shown in FIG. 17, as the case may be, there is the possibility that it takes an unrealistic processing time to gain a solution because the above technique needs a lot of computations. Needless to say, by narrowing the service area to be taken as an object of design, the AP number that has to be arranged is reduced, which enables a reduction in the processing time; however the base station number to be arranged per area becomes extremely numerous in a picocell environment like the wireless LAN, as compared with a macrocell/microcell environment in the conventional mobile communication system, whereby the problem occurs that the size of the area that can be designed within the realistic processing time does not come up to the necessary size of the area by far.
In other words, in designing the picocell system, a difficult task has to be tackled of coping with an increase in a base-station layout density while a radio-wave analysis, which requires a lot of the computations and is of high precision, is employed, that is, it is indispensable to achieve the fast base-station cell design algorithm.
Upon employing the base-station cell design technique disclosed in the patent document 1, the computation time can be reduced because a human being pre-narrows down the location candidates. However, the result varies anyway, depending upon the AP layout candidate selected firstly, and vague elements such as a perception and an experience of a designer dictate the selection of the AP layout candidate, thus the problem existed that an appropriate cell design was not always possible to guarantee.
The vagueness of the perception/experience of the designer can be excluded in the base-station cell design technique disclosed in the patent document 2; however it was pointed out that the solution did not converge, depending upon pre-setting of parameters such as initial layout, which gave rise to occurrence of an unstable phenomenon such as divergence and oscillation, and the problem existed that if there rose the situation where the convergence of the solution was unpromising, a work had to be done over again from the beginning.
In the base-station cell design technique disclosed in the non-patent document 1, there is no vague element like one shown in the patent document 1 at the time of the design, and also, such an unstable phenomenon shown in the patent document 2 does not occur. However, the base station number to be pre-determined, which is required for making an effective cell-layout design, is more than several tens of times as large as the base-station number to be determined finally. Thus, when the radio-wave analysis is made in terms of the plane in details within the service area with all candidate points thereof taken as a transmission point, after all is said and down, the enormous computation time is necessitated.
Also, either of the above-mentioned prior arts, which are for aiming only for optimization of the layout of AP, have no setting method of various design parameters (a transmitted electric power, channel allocation, etc.) shown. Also, in the event of making wide-range development by a plurality of the stations, an offset of the traffic density that depended upon the location becomes noticeable; however no traffic density was reflected in the cell design in either of the above-mentioned prior arts.